The invention is based on patent application No. 11-249044 Pat. filed in Japan, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a method of forming a light emitting portion of a light spot forming device and an optical element.
2. Description of the Background Art
In an optical memory device for optically recording and reading information, an optical recording medium is used, and a light spot is emitted from a light head to the optical recording medium for recording and reading information so that the information (marks) is recorded on the medium or is read from the medium.
In a field of an optical memory device for optically recording and reading information, it has been demanded to provide a light head which can remarkably increase a capacity of information recorded on the optical recording medium and thus can remarkably increase a record density of information on the optical recording medium because operation speeds of computers have been increased and/or multimedia has been developed. For satisfying the above demand, an optical memory device which is provided with a light spot forming device (light head) using near-field light has been proposed.
In a conventional optical memory device which does not use near-field light, but uses ordinary light, the maximum record density of information depends on diffraction limit of light, and it is impossible to record and read marks substantially shorter than about 300 nm which is substantially equal to the wavelength of light.
In contrast to the above, the optical memory device which has recently been proposed utilizes near-field light and thus a near-field phenomenon of light. In this optical memory device, a minute light spot of a size smaller than the light wavelength is formed, and a distance between the light head and the optical recording medium is reduced to tens of nanometers for information recording and reading. Thereby, small marks of 200 nm or less in size, which exceed the light diffraction limit, can be written (recorded) on the optical recording medium, and can be read therefrom.
The light spot forming device which uses a probe utilizing an optical fiber, a Solid Immersion Lens (SIL) or the like has been proposed as means, which is used for forming a light spot in a light head of an optical memory device using near-field light for writing and reading information. This light spot forming device usually has a light emitting portion which has a light collecting portion utilizing an optical fiber or the like and a minute opening neighboring to it.
In a process of making the light spot forming device, the minute opening is formed in a base member of the light emitting portion. For example, a material which can intercept the light is arranged on the base member of the light emitting portion, and an appropriate light source emits laser light with a high power to the light intercepting material. Thereby, the minute opening is formed.
However, in the process of forming the minute opening in the base member of the light emitting portion of the light spot forming device, the light spot forming device having the light emitting portion, which is provided with the minute opening formed on the end surface of the optical fiber, suffers from such a problem that the position of the minute opening formed in the light emitting portion cannot be accurately coincident with the position of light sent through the fiber from the light source for light spot formation without difficulty. Also, the light spot forming device having the light emitting portion, which is provided with the minute opening in the position of focus of the light collecting portion, suffers from such a problem that the position of the minute opening formed in the light emitting portion cannot be accurately coincident with the position of light collected by the light collecting portion without difficulty.
An object of the invention is to provide a method of forming a light emitting portion of a light spot forming device, which has the light emitting portion having a minute opening for emitting a light spot, and a light collecting portion neighboring to the light emitting portion for collecting the light coming from a light source for light spot formation to the minute opening, and particularly is to provide the method, in which the position of the light collected by the light collecting portion can be accurately coincident with the position of the minute opening in the light emitting portion, and besides, the light emitting portion can be simply and easily obtained.
Another object of the invention is to provide an optical element which can be used for implementing the method according to the invention.
For achieving the above objects, the inventor has earnestly made a study to find out the followings. In the light spot forming device, the light emitted from the light source for light spot formation is collected by the light collecting portion at a specific position on the base member of the light emitting portion. In this position, the minute opening is formed. In other words, this position can be utilized as the reference for positioning the minute opening to be formed. Thereby, the position where the light is collected by the light collecting portion can be accurately coincident with the position of the minute opening, and the light spot can be efficiently generated.
The invention has been developed based on the foregoing finding, and provides first and second methods of forming a light emitting portion of a light spot forming device as well as an optical element.
(1) First Method of Forming a Light Emitting Portion of a Light Spot Forming Device
A method of forming a light emitting portion of a light spot forming device having the light emitting portion having a minute opening for emitting a light spot, and a light collecting portion neighboring to the light emitting portion for collecting the light coming from a light source for light spot formation to the minute opening, including the steps of:
forming a light emitting portion base film, which allows partial passage of the light coming from the light source for light spot formation, in a light collecting region portion, which is to be adjacent to the light emitting portion, of the light collecting portion;
forming on the light emitting portion base film a resist film allowing partial passage of the light coming from the light source for light spot formation, being substantially insensitive to the light coming from the light source and being sensitive to predetermined light for resist exposure;
arranging a light intercepting mask provided with a through-hole and a light amount detecting device in this order in an area opposed to the resist film;
adjusting the position of the light intercepting mask along the resist film such that the light coming from the light source for light spot formation is collected by the light collecting portion onto the light emitting portion base film, and is received by the light amount detecting device through the light emitting portion base film, the resist film and the through-hole in the light intercepting mask, and the amount of light detected by the light amount detecting device takes on the maximum value;
exposing the resist film with the light coming from a light source for resist exposure through the through-hole in the light intercepting mask in the adjusted position;
forming a through-hole for etching by removing an exposed portion of the resist film;
forming the minute opening in the light emitting portion base film to provide the light emitting portion formed of the light emitting portion base film by effecting etching on the light emitting portion base film through the through-hole for etching in the resist film; and
removing the resist film.
(2) Second Method of Forming a Light Emitting Portion of a Light Spot Forming Device
A method of forming a light emitting portion of a light spot forming device having the light emitting portion having a minute opening for emitting a light spot, and a light collecting portion neighboring to the light emitting portion for collecting the light coming from a light source for light spot formation to the minute opening, including the steps of:
forming a light emitting portion base film, which allows partial passage of the light coming from the light source for light spot formation, in a light collecting region portion, which is to be adjacent to the light emitting portion, of the light collecting portion;
forming on the light emitting portion base film a resist film allowing partial passage of the light coming from the light source for light spot formation, being substantially insensitive to the light coming from the light source and being sensitive to predetermined light for resist exposure;
arranging a projection lens, a half mirror and a light intercepting mask provided with a through-hole in this order in an area opposed to the resist film, arranging a light amount detecting device near the half mirror, and determining a positional relationship between them such that an image of the through-hole in the light intercepting mask is formed by the projection lens on the resist film, and the light coming from the projection lens side and reflected by the half mirror toward the light amount detecting device is collected to the light amount detecting device;
adjusting the position of the light collecting portion such that the light coming from the light source for light spot formation is collected by the light collecting portion onto the light emitting portion base film, and is received by the light amount detecting device through the light emitting portion base film, the resist film, the projection lens and the half mirror, and the light amount detecting device detects the amount of light indicating the fact that an image of the through-hole in the light intercepting mask is formed in the same position on the resist film as the light collected by the light collecting portion;
exposing the resist film with the light coming from a light source for resist exposure through the through-hole in the light intercepting mask, the half mirror and the projection lens;
forming a through-hole for etching by removing an exposed portion of the resist film;
forming the minute opening in the light emitting portion base film to provide the light emitting portion formed of the light emitting portion base film by effecting etching on the light emitting portion base film through the through-hole for etching in the resist film; and
removing the resist film.
(3) Optical Element
An optical element including:
a light incoming portion for receiving coming light;
a light emitting portion for emitting the light coming from the light incoming portion;
a reflection film for reflecting and collecting the light coming from the light incoming portion to the light emitting portion; and
a light intercepting film having a light transmittance of 0.001% to 10%, and covering the light emitting portion for partially passing therethrough the light emitted from the light emitting portion.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.